Are they saving bucks?
The time it takes even a bottom rate driver on straight time to restart over and over again has got to be adding up. Let alone top rate on overtime.
From a technical perspective, it's mostly the radio hardware that you can't get around.
Building an embedded system stack that can do everything that the diad can wouldn't be a huge deal for someone as big as UPS.
But in order to have it have wireless capabilities, you're going to essentially need a preexisting OS that Qualcomm, Samsung, and the other cellular chip makers have provided support for.
It's very secretive, and even on open platforms, support is generally provided by the manufacturers in the forms of compiled "blobs". This is why even Linux based platforms could be subjected to government or other entity backdoors.
Long story short, it's way easier to piggyback off of Android and let other massive companies pay for all the platform development, while they only need to focus on a single app.